Steel transport wheels and steel rails have many issues that require the control of friction between the two surfaces. Failure to control the friction in a positive manner can result in noise problems, extensive wear and sub-optimum performance (from an efficiency standpoint) caused by slip-stick oscillations due to negative friction between the two sliding steel surfaces. Accordingly, friction modifiers with high and positive friction to control sliding and rolling-sliding contact in steel-rail and steel-wheel transportation systems are well known in the art. Various patents from Kelsan Technologies describe friction modifier compositions (see, U.S. Pat. Nos. 6,759,372; 6,855,673; 7,045,489; 7,160,378; 7,244,695 and 7,939,476). These patents describe a water-based system commercialized by Kelsan.
However, there are various problems with some of these water based friction modifier products. Examples of the problems are set out below:
When ammonia is used in the water-based systems it can cause equipment to rust. Latex can cause problems with the gears and other movable mechanical parts as the compositions dry out. These compositions can form a skin over the liquid when it is pumped onto the rail head and the product is allowed to dry before taken up by a train wheel in a short period of time, and this can cause flowing out or splashing when contacted by the wheels of the train and accordingly not be carried down the track by the wheels of the train.
What is needed is a friction modifier composition for top of rail applicators that help prevent rust on equipment with which it comes into contact.
Another object of the invention is to eliminate the latex skin on the prior art compositions such that the product when applied does not have a skin but instead forms a soft, non-drying deposit on the rail head. This soft non-drying deposit is picked up by the train wheel and carried down the rail to form a continuous film which controls the friction between the wheel and the rail in a positive manner.
In accordance with a further object of the invention, the friction control composition is embodied as a thixotropic gel or liquid that is thinned by shear and returns to its thicker more viscous state under static conditions. The thixotropy of the composition is used to facilitate application to the rail and to promote retention on the rail in its thicker state without formation of a skin. Unlike the prior art compositions discussed above, the composition does not form a skin over a low viscosity fluid that is ejected or pushed away by the rolling contact of the train wheels. Thus, the composition may be mixed for liquid-like flow during application to the rail as by conventional rail-mounted pump systems. Following rail application, the composition thickens under static conditions without drying or forming a skin, and remains positioned on the rail until sheared by train wheel engagement for distribution along the track during “carry down”.
Another object of the invention is to have freezing point depressant that does not degrade the rheology of the composition.
Yet another object of the invention is to have a composition that causes the thickener (e.g. the clay) to go into a matrix such that it has improved dispersability.
Also, solid stick prior art compositions, such as the one described in, U.S. Pat. No. 4,915,856, are well known in the art. But these solid stick friction modifiers have their own problems such as expense, and they need mechanical brackets and applicators to apply the product to the wheel. With solid stick compositions, practicality of use and duration of efficacy can also be a problem on freight trains.
Another object of the invention is to change the sliding friction from negative to positive.
Another object of the invention is to reduce noise by reducing or eliminating slip-stick oscillations between the wheel and rail.
Another object of the invention is to reduce lateral creep, which reduces lateral forces by changing the friction from negative to positive between the wheel and rail when a train, especially a freight train, goes through a curve. The benefits of reducing lateral forces include increasing the stability of the train as it travels down the track and in a related manner there is a reduction of the wear on the rail head, rail ties, and tie plates. Also, the bogey or truck goes around the curve in a much smoother fashion with reduction in jerking and jumping movement.
Another object of the invention is to reduce longitudinal creep wherein the wheel is sliding forward such as occurs in a transit system when the wheel is going around a mild curve. In longitudinal creep, if the wheels go slightly off-kilter, the locomotive pulls the wheel and the wheel slides in the longitudinal direction. If this creep happens all the time, you get short pitch corrugations. These are wear marks on the rail head in the nature of corrugations as encounter in a dirt road. By reducing this creep, the wheel will not slide as far and short pitch corrugations are inhibited.
Another object of the invention is to reduce spin creep wherein there is instability between the wheel and the rail, and the wheel is almost making a small circle on the top of the rail head.
The friction control compositions of the present invention reduce, if not eliminate, these three different types of creep by changing negative friction to positive friction. Lateral forces are one of the main problems in the heavy haul railroad in North America, and it is preferably reduced in accordance with the present invention. Similarly, longitudinal creep is reduced, if not eliminated, in order to inhibit the formation of short pitch corrugations in the rail. The reduction or elimination of spin creep is also desirable in order to reduce wear on the wheel and rail.
All of these creeps are small and are, for example, in the micron size range. The friction control compositions herein are effective to change the friction from negative to positive and thereby reduce or eliminate creep and the accompanying stick-slip.